1. Field of the Invention
The present invention relates to techniques for accessing channels in networks. More specifically, the present invention relates to scheduling techniques for use with dynamic channel-access protocols.
2. Related Art
Recent advances in networking technology have made it possible to support multiple voice-related applications, such as mobile smart phones and Voice over Wireless Internet Protocol (VoWIP), on individual networks. In the near future, these applications may be running on mobile stations concurrently with legacy data-centric applications. To support such integrated voice/data traffic in a network, the channel-access protocol (such as the Medium-Access-Control protocol) in these systems needs to provide high channel utilization and bounded channel-access delay. The former is important for data-centric applications, and the latter is critical for providing uninterrupted data delivery in voice-related (i.e., real-time) applications.
Contention-based channel-access schemes have previously been developed for multiple-hop ad-hoc networks and for wireless local area networks or LANs. However, these existing approaches are unable to provide high channel utilization as network load increases. In addition, ad-hoc networks that utilize such conventional channel-access schemes are vulnerable to collisions, which can potentially starve certain stations by preventing them from acquiring the channel. As a consequence, the existing contention-based approaches are unable to ensure an upper bound on the channel-access delay. This makes it impossible to run soft real-time applications, and even bulk transfer applications, over these networks at high loads.
‘Contention-free’ schemes have been proposed to overcome these limitations, thereby providing conflict-free channel access independently of the radio connectivity around any given device or node in the communication system. These contention-free schemes may be classified as ‘topology independent’ and ‘topology dependent.’ In topology-independent channel-access schemes, deterministic transmission schedules are produced that allow nodes or devices in an ad-hoc network to periodically access the communication channel without collision and also ensure a bounded channel-access delay. For example, a device may be pre-assigned one or more unique sub-channels (such as time slots) in a global schedule. However, these contention-free schemes typically require an excessive amount of control-signaling overhead and global knowledge of the network, and typically also suffer from channel under-utilization.
In contrast, topology-dependent channel-access schemes use local topology information to produce the transmission schedules. These schemes may be used to construct schedules for small groups of devices, thereby solving the under-utilization problem at high loads while only using small-area topological knowledge. For example, dynamic (randomized) channel-access schemes use probabilistic transmission schedules in which each device always has a certain probability to access the channel during a given sub-channel.
Unfortunately, while such techniques incur less control overhead than the earlier contention-free channel-access protocols, they still do not ensure a bound on channel-access delay. In particular, as the number of devices competing for sub-channels increases in the communication system, the probability of any given device winning an election for a sub-channel goes down.
Hence what is needed is a method and an apparatus that facilitates channel-access in networks without the problems listed above.